OCR Text |
Show -10- solution flow at loads of 155 MW (see Figure 13). Solution flow rates of 16 gpm (1 gpm per injector) represent deSign conditions. At full load, increasing the dilution water flow from about 14 to 18 gpm reduced NOx emissions by about 9 percent (0.35 Ib/MMBtu to 0.32 Ib/MMBtu). This decrease in NOx emissions was not, however, without side effects. Figure 14 shows that NH3 Slip increased with increasing solution flow. The increase, relative to design flow conditions, was 22 ppm (from 5 ppm to 27 ppm). These changes in performance can be explained by changes in mixing brought on by increased solution flow. As solution flow increases, at a fixed NSR, droplet momentum increases and solution concentration decreases. These changes combine to provide better mixing and increase droplet evaporation time, which move the chemical release point to cooler temperature regions. The improved mixing leads to lower NOx emiSSions, while transporting the chemical to cooler zones increases NH3 Slip. Based on these tests, a solution flow of 1.0 gpm was selected for normal operation. NOx emissions are plotted versus NSR in Figure 15 for tests performed at 155 MW. These data show that NOx emissions decreased with increasing NSR, as expected. NOx emissions decreased from 0.36 Ib/MMBtu at an NSR of 0.4 to 0.29 Ib/MMBtu at an NSR of 1.3. Of special significance is the NSR at which NOx emissions could be maintained at 0.3 Ib/MMBtu. This was the desired operating target to provide a margin relative to the regulatory limit of 0.33 Ib NO; MMBtu. This NSR was found to be about 0.8 for these operating conditions. The NH3 slip data are plotted versus NSR in Figure 16. These data show that NH3 slip increased with NSR. At an NSR of 1.3, NH3 slip was about 2 ppm. This slip level is low relative to the desired operating level of 5 ppm NH3 Slip. Test results also showed that increases in CO emissions were less than 15 ppm at an NSR of 1.5 for the loads tested. Figure 17 shows the ratio of N20 production to NOx reduction plotted versus NSR. The data show that this ratio increased with NSR, ranging from about 17 percent at NSR = 0.4 to 21 percent at NSR = 1.3. |